1. Field of the Invention
The present invention relates to a composite structure, a fabric form to be used for the composite structure, and a multilayer fabric from which the fabric form is made. The composite structure of the present invention is formed by inserting, into the fabric form, pulverized or granular matter like soil or sand, inorganic matter, liquid or gaseous matter, or a mixture of the same, the fabric form restraining the same.
2. Description of the Related Art
A fabric form in which soil, sand, concrete, or the like is inserted between two layers of fabric has hitherto been known as a means to obtain a composite structure. However, a composite structure made of a conventional fabric form has disadvantages of unsatisfactory strength, thickness, i.e., distance between the two layers of fabrics, and appearance and several other problems. For example, a composite structure made of a conventional fabric form has a surface having large convex portions and large concave portions, i.e., it is impossible to obtain a flat surface of the composite structure. Further, since the difference between the maximum thickness and minimum thickness is large, the strength of the composite structure is irregular, being particularly low at the locations of minimum thickness. To obtain sufficient strength of the minimum thickness portions, the thickness of the maximum thickness portion is unnecessarily increased. The result is a larger quantity of material used for the fabric form and thus a higher cost. Further, there is a limit to the thickness of the conventional fabric form and it is difficult to make a composite structure having a very large thickness.
The above disadvantages of the conventional composite structure are caused by the constitution of the conventional fabric form, more exactly, the constitution of the multilayer fabric forming the conventional fabric form. A variety of multilayer fabrics have been proposed. One is obtained by connecting an upper layer fabric and a lower layer fabric at predetermined longitudinal and lateral intervals by suitable connecting members, e.g., bolts or strings. Though the thickness of this multilayer fabric can be adjusted to a large extent by adjusting the length of the connecting members or the longitudinal and lateral intervals, it is not easy to get a uniform thickness by this type of adjustments. For example, when strings are used as the connecting members 6 as illustrated in FIG. 40, since a knotting portion 51 of the strings is easily elongated, it is impossible to obtain exactly the desired thickness of the multilayer fabric or therefore, uniformity of the thickness. Further, the strength of the multilayer fabric near the point where the connecting member is attached is low, so the multilayer fabric easily breaks, and the thickness of the multilayer fabric becomes even more irregular and an appearance of the multilayer fabric becomes inferior. Further, productivity of this multilayer fabric is extremely low.
Another conventional multilayer fabric comprises layers of distinct fabrics connected together at predetermined longitudinal and lateral intervals by connecting yarns. A conventional weaving machine is unable to produce such a multilayer fabric having a sufficiently large thickness. The thickness of a multilayer fabric obtainable on a conventional weaving machine is, at most, several tens of millimeters, assuming normal longitudinal and lateral intervals. In order to construct a multilayer fabric sufficiently expandable in thickness when filled, therefore, the practice has been to connect the layers of the component fabrics at greater longitudinal and lateral intervals. This multilayer fabric, when filled, expands in thickness and contracts in area, making the surface irregular and spoiling the uniformity of thickness. Then, the large thickness of the multilayer fabric filled is caused by making largely expanded convex portions between the longitudinal and lateral intervals. This is undesirable in respect of ease of handling and the quality of the fabric form (the filled multilayer fabric). For example, since this multilayer fabric shrinks when filled, it is necessary to hang the fabric form from a chain block, fill it until it reaches the desired size, then lower it for use. Further, connection between each fabric form of this multilayer fabric is extremely difficult and considerable time is necessary for filling.
U.S. Pat. No. 3,811,480 discloses a multilayer fabric intended to solve some of these problems of the multilayer fabric. In this multilayer fabric, as illustrated in FIG. 41, the connecting warps for connecting the layers of the fabrics are inserted in loops. As a result, the length thereof is greater than that of the ground warp extending on the ground portions of the fabrics. After weaving, the layers of the fabrics are pulled apart by inserting a jig or by filling so that the loop portions of the connecting warp are drawn out between the layers of the fabrics (see FIG. 42).
In actuality, however, the loop portions of the connecting warp frequently remain held between the warp and wefts in the ground portion, i.e., it is difficult to completely draw out the loop portions. Therefore, it is difficult to obtain a constant length of the connecting warp between the fabrics. To deal with this problem, the ground warp near to the connecting warp are usually designed to have a low warp density so that the loop portions of the connecting warp can easily slide between the ground warp near to the connecting warps. In this case, however, the connecting warp become unfixed in relation with the ground weave and in some cases will slide relative to the ground weave when the expanded multilayer fabric is handled or when the fabric form made of the expanded multilayer fabric is being filled, again resulting in irregular thickness of the obtained composite structure.
Further, since the loop portions of the connecting warp are made by overfeeding the connecting warp to the ground weave, a coarse warp cannot be used as the connecting warps. As a result, a fabric form having a high pressure resistance cannot be obtained, and it is necessary to perform the filling at a relatively low pressure. This means a composite structure of a high density and a high strength cannot be obtained.
Even if this multilayer fabric is used, to enhance the thickness expandability of the fabric, it is necessary to increase the longitudinal and lateral intervals between the connected portions to increase the loop length of the connecting warp s. Therefore this multilayer fabric has the same disadvantages as the former multilayer fabric in respect to ease of handling and quality when filled. Further in this multilayer fabric, since it is impossible to use the thick connecting warp to make the same to easily slide against the ground warp near to the connecting warps, it is impossible to make the multilayer fabric having high pressure resistance. Therefore when this multilayer fabric is used as the fabric form, a filling pressure should be low pressure. It means that a composite structure having high density and high strength cannot be obtained.